Processes for manufacturing alkylene carbonates are already well known. One such method involves the reaction of an epoxide with carbon dioxide in the presence of proper catalysts. Another method is bases on the reaction between vicinal glycols and phosgene. Still another method is based on the reaction between vicinal halohydrins and sodium bicarbonate in the presence of carbon dioxide.
Such metods as these, however, have the drawback of involving, respectively, rather high working temperatures and pressures, or the use of toxic reagents (phosgene), or of giving rise to the collateral formation of undesired by-products that are difficult to separate (glycols).
From U.S. Pat. No. 3,923,842 it is also known how to prepare alkylene carbonates by reacting vicinal halohydrins with carbon dioxide, in a solvent and in the presence of amines, according to the reaction scheme: ##STR2## wherein R, R.sub.a, R.sub.b, R.sub.c and R.sub.d, like or unlike one another, are hydrogen, or alkyl, aryl, alkylaryl or arylalkyl radicals, and where X is a halogen. This process, although offering considerable advantages in respect of the above-cited methods, does not seem fully satisfactory, inasmuch as the reaction develops rather slowly even at high temperatures (70.degree.-100.degree. C.) and requires the use of high carbon dioxide pressures to obtain appreciable results from an industrial viewpoint.